The present invention relates to a fastening system including two-piece swage fasteners and more particularly to pull type swage fasteners with the present invention directed to a construction in which the tensile or relative axial loads required to swage the fastener are reduced permitting the use of smaller, lighter weight installation tools while providing a fastener having a preselected strength and a desirable weight and size.
The present invention relates to two-piece swage type fasteners or lockbolts generally of the type illustrated in U.S. Pat. No. 2,531,048 to L. Huck, issued Nov. 21, 1950, and U.S. Pat. No. 3,215,024 to Brilmyer et al issued Nov. 2, 1965; there are numerous other variations of swage type fasteners such as U.S. Pat. No. 3,915,053 to J. Ruhl, issued Oct. 28, 1975, U.S. Pat. No. 4,472,096 to J. Ruhl and R. Dixon, issued on Sep. 18, 1984 and U.S. Pat. No. 5,090,852 to R. Dixon, issued Feb. 25, 1992.
In many commercial applications, two-piece threaded or swaged fasteners are used and are designated by a grade indicative of a particular strength level. For example, a 5/8 inch Grade 5 fastener will have a 5/8 inch diameter pin or bolt shank portion for use in a nominal 5/8 inch diameter workpiece opening and will have a strength level indicated by the grade level, i.e. Grade 5. A Grade 8 bolt, on the other hand, will have higher strength characteristics than the Grade 5 bolt while a Grade 9 bolt will have even higher strength characteristics. For example the strength of a Grade 5 fastener is determined by the strength of the material of the bolt or pin as set by SAE J429 or ASTM A-325 with a minimum material tensile strength of 120 KSI while a Grade 8 is set by SAE J429 or ASTM A-490 at 150 KSI.
A typical swage type fastener includes a pin and a collar with the pull type fastener having a pin shank having a locking portion with lock grooves and a pull portion with pull grooves. The pull grooves are adapted to be gripped by matching teeth in chuck jaws of an installation tool having a swage anvil adapted to engage the collar whereby a relative axial force can be applied between the pin and collar to move the anvil over the collar to swage it into the lock grooves. Here the relative axial force is a tensile load on the pin via the chuck jaws and a compressive load on the collar via the tool swage anvil.
In many swage fasteners the pull portion is connected to the lock groove portion by a breakneck groove of reduced strength which is adapted to fracture at a preselected magnitude of axial or tensile force greater than that required to swage the collar whereby the pull portion, or pintail, will be severed and removed from the pin shank after completion of swaging. Other swage fasteners, however, have pull portions which remain on the pin after completion of installation. See for example U.S. Pat. No. 5,315,755 to Fulbright et al, issued May 31, 1994 where a threaded pull portion is utilized which is not severed from the pin.
In many instances, with swage fasteners of relatively high strength, in order to fully swage the collar the magnitude of applied tensile load can be quite high requiring an installation tool of relatively large size and weight. This is especially significant where manually operated installation tools are used. Such tools typically include hydraulic and/or pneumatic piston-cylinder constructions the size and weight of which will vary with the necessary magnitude of tensile load to be applied. Such tools can be of the type shown in U.S. Pat. No. 4,597,263 to R. Corbett issued Jul. 1, 1986 and U.S. Pat. No. 4,878,372 issued Nov. 7, 1989 to Port et al.
In addition with fasteners including pins having the pull grooves on a severable pintail the breakneck groove must also be of sufficient strength to withstand the high tensile load for swaging and the pull grooves must be similarly of sufficient strength to accept the relative axial pull load applied by the engaged teeth of chuck jaws on the installation tool. This routinely requires that the pull portion be of a relatively large diameter so as to have sufficient material to provide the necessary size and strength for the breakneck groove and also to inhibit fracturing of the pull grooves instead of the breakneck groove. This also adds to the size and weight of the components of the tool to engage the pull grooves and to provide the tensile load on the pin for fracture of the breakneck groove.
In the present invention, a two-piece swage type fastener is provided which can be installed at a lower swage load than a conventional swage type fastener of comparable grade but when installed has the physical properties of essentially the same values such as tensile strength, clamp load and the like on the workpieces being connected. This permits the use of a smaller, lighter weight installation tool in comparison to similar swage type fasteners having the same Grade capability for providing similar physical properties. At the same time with pins having a severable pintail, the breakneck groove and pull grooves can be correspondingly reduced in strength. This permits the pull portion or pintail of the pin shank to be reduced in diameter thus reducing the amount of metal in the pin and at the same time reducing the weight and material cost. The reduced diameter pintail also facilitates the manufacture of the lower strength breakneck groove by roll forming.
However, with pull type swage fasteners having threaded pull portions which are not severed, as in the '755 patent, supra, the present invention facilitates the engagement of fewer threads on the pull portion since the extra force required to fracture a breakneck is not required. This causes less stress on the engaged threads of the mating threaded thimble or nut member on the pull tool resulting in longer life. This also permits the use of a shorter, less expensive pin since less pin protrusion is required for the fewer pull grooves to be gripped. Also the installation tool can be smaller and hence lighter and less expensive since lower applied loads are required for final installation. This also facilitates the use of an internal drive of the type illustrated in FIGS. 17 and 18 of the '755 patent which as shown involves the use of a threaded pull rod or spindle engageable with pull grooves provided by a threaded bore in the end of the shank of the pin or bolt. The use of an internal drive will permit a reduction in protrusion relative to the external drive thereby providing for a more efficient final fit and appearance.
One form of a conventional swage type fastener is shown herein in FIGS. 7 and 7A. This type of fastener is used primarily in industrial applications such as buildings, bridges, trucks and the like. Such fastener also requires the application of a relatively high axial force for swaging and for final installation and accordingly requires a relatively large and heavy installation tool. Thus, in the present invention, the swage type fastener which comprises a pin and a collar is for use in applications similar to that of the fastener of FIGS. 7, 7A but, in contrast, the pin and collar are adapted to be set at a relatively low axial force and with a substantially smaller and lighter weight tool.
In one form of the invention the lock grooves in the pin are constructed to have wide or elongated roots which are of a simulated streamlined shape generally as shown in the '852 patent (supra). The crests of the shoulders of the lock grooves are contoured to facilitate the flow of the collar material as it is swaged to reduce the magnitude of tensile or swage load required to swage. Also the lock grooves are substantially wide relative to the width of adjacent crests which further promotes the flow of collar material during swage. As will be seen, however, the overall structure and operation of the fastener of the present invention is substantially different from that of the '852 patent and its commercial form. In this regard, and as previously noted, the fastener of the present invention is primarily designed for use in applications such as those of the conventional form shown in FIG. 7 which are lower strength and require lower installation loads than those of the fastener of the '852 patent. Thus the collar of the present invention is provided with a predetermined wall thickness, and hence volume, not only to provide a preselected amount of fill of the roots of the lock grooves during swaging but also to provide a retained clamp load or force having a magnitude which is considerably higher than the installation load. In this regard, unlike the fasteners of the '852 patent, the amount of fill of the lock grooves by the swaged collar, while substantial, is less than complete leaving a desired clearance at the base of the roots; this acts to prevent compression of the collar material against the root during swaging and thereby assists in minimizing the required installation loads. In addition the diameter of the collar bore is minimized to provide a relatively close clearance fit with the crests of the lock grooves of the pin and at the same time the outside collar diameter is selected to provide a selected, desirable volume of the swageable portion of the collar. The preceding features are significant in facilitating swaging of the collar material into the wide lock grooves in the pin at a lower relative axial force. At the same time the subject fastener will provide clamp loads which are of a significantly higher magnitude than the installation loads whereas with the conventional or prior swage type fasteners the same magnitude of clamp loads require substantially higher installation loads.
In addition to the above, the swage cavity of the installation tool has a configuration which assists in providing swaging at reduced relative axial or installation loads. At the same time the engaged end of the collar shank is configured to cooperate with the swage cavity construction and compensate for the minimized clearance to provide a desired magnitude of resistance to initiation of swaging or snubbing resulting in a relatively high desired magnitude of initial hold-off load to provide sufficient pull together of the workpieces to eliminate any gap between them.
In one form of the present invention the pin lock grooves are of a substantially greater width than the width of the crests while the collar is no longer than that required by a collar for a comparable, conventional fastener such as shown in FIGS. 7, 7A to provide filling of sufficient grooves and resultant engagement of the appropriate number of pin and collar shoulders to provide the desired design tensile load. In this way, the number of pin crests per unit of length over which the collar is swaged is substantially reduced assisting in the minimization of the relative axial force or swage load for swaging. At the same time the large width and contour of the grooves facilitates flow of the collar material during swage.
With the present invention swage loads and thus the related relative axial loads required for swage have been reduced by at least around 25% to around 45% in comparison to prior pull type swage fasteners such as shown in FIGS. 7, 7A of comparable size and strength while providing fastened joints with substantially the same magnitude of final clamp load or force. In addition, in one form of the invention, the final magnitude of clamp load attainable can be around 1.5 to around 1.9 times the magnitude of the applied swage load whereas for fasteners of the same size and grade the prior conventional swage fasteners achieve a final clamp load or force around 1.2 to 1.3 times the swage load. Of further importance is that the installation tool can be substantially reduced in size and by around 45% in weight. With severable pintailed fasteners the final installation load requires some increase over the final swage load but here with the lower swage loads the fracture loads of the breakneck grooves can be reduced. The lower installation loads and reduced pin break load in addition to reduction in tool size and weight also results in substantially less shock load to the operator.
While the present invention is shown and described for pull type swage fasteners, it should be understood that there would be benefits of the low swage load fastener that would be realized by stump type swage fasteners which are generally installed by squeeze type tools. See for example the stump type fastener in FIG. 1 of the '096 patent, supra.
As previously noted the benefits for the swage type fasteners with non-severable threaded pull portions are additionally significant since the extra force or load for pin break is not required. In addition and in order to further enhance the strength of the threaded type pull grooves, a modified thread form has been provided which further reduces the number of threaded pull grooves that need to be engaged by the threaded thimble or nut member to sustain the necessary pulling force to attain the lower installation loads.
In addition, a unique system has been provided to facilitate the use of the internal drive noted resulting in certain additional advantages.
Also, in one form of the fastening system, a swage anvil having a unique swage cavity is provided which is especially useful with the form of the fastener having external combined helical lock and pull grooves and the fastener having the internal pull grooves. Here the swage cavity not only facilitates swaging but also assists in removal from the collar over the portion of the collar which tends to spring back after swage.
Thus it is an object of the present invention to provide a fastening system including a novel two-piece swage type fastener having a collar of a preselected wall thickness and volume and minimal clearance relative to the crests of the lock grooves of the pin resulting in a reduced magnitude of installation and/or swage load required to be applied to install the fastener.
It is another object of the present invention to provide the collar with a selected volume relative to the volume of the elongated roots of the lock grooves whereby the swaged collar material does not completely fill the lock groove roots which are generally shallow.
It is an object of the present invention to provide a novel two-piece swage type fastener in which the pin has a severable pintail and with the fastener being installed at a reduced tensile load whereby the pintail can be of reduced size.
It is another object of the present invention to provide a fastening system including a unique two-piece swage type fastener in which the pin has a threaded pull portion which is not severable and with the fastener being installed at a reduced tensile load whereby the number of engaged threads necessary for the swage load to install the fastener can be reduced and whereby the loads on the threads of the pull grooves and of the mating nut member or mating threaded spindle on the installation tool are reduced.
It is another object of the present invention to provide a fastening system including a unique swage type fastener including a pin and collar and an installation tool having a swage cavity with a preselected contour relative to the collar whereby the relative axial loads required for swaging of the collar are reduced permitting the use of a relatively small, lightweight tool while providing an installed fastener of comparable strength relative to conventional swage type fasteners of the same Grade.
It is another object of the present invention to provide a novel two-piece swage type fastener capable of being installed at substantially reduced relative axial loads and in which the pin has lock grooves of a generally helical contour.
It is another object of the present invention to provide a fastening system including a novel two-piece swage type fastener capable of being installed at substantially reduced relative axial loads and in which the pin has pull grooves of a generally helical contour and of a unique configuration to withstand the necessary installation loads.
It is another object of the present invention to provide a fastening system including a unique two piece swage type fastener capable of being installed at substantially reduced relative axial forces utilizing an internal drive.
It is still another object of the present invention to provide a fastening system including a swage anvil having a unique swage cavity.
It is another, general object of the present invention to provide a unique fastening system including a novel two-piece swage type fastener.
Other objects, features and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, in which: